Fractionation of hydrocarbons utilizing flow controls responsive to temperature



Sept. 5, 1967 D. R. BATES 3,340,158 FRACTIONATION OF HYDROCARBONS UTILIZING FLOW CONTROLS RESPONSIVE TO TEMPERATURE Filed May 26; 1964 v a (u 9 Q (S g v? i a 9] N T m 8 I Q N N d.) 8 Q) E d) u) OI 9 2 L 8 a l l 7 2 3 INVENTOR. 5 D. R. BATES 7 M W ,4 rromvsrs United States Patent FRACTIONATION 0F HYDROCARBONS UTI- LIZING FLOW CONTROLS RESPONSIVE T0 TEMPERATURE Donald R. Bates, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 26, 1964, Ser. No. 370,162 7 Claims. (Cl. 2032) This invention relates to apparatus for fractionation. This invention also relates to a method of fractionation.

In one of its aspects, this invention relates to temperature control in a secondary fractionator and an accumulator which is not associated directly with said secondary fractionator by splitting the overhead from a primary fractionator which is directly associated with said accumulator, passing at least part of the split overhead either directly to said accumulator or through a primary heat exchange zone and then to asid accumulator while passing other parts of said split overhead to a secondary heat exchange zone associated with the secondary fractionator and then passing he ouflow from said secondary heat exchange bone either directly to said accumulator or through the primary heat exchange zone to said accumulator or both. In one of its aspects, this invention relates to the control of fractionator overhead as above wherein the flow of part of the split overhead to the secondary heat exchange zone is controlled by flow control means which responds to flow variations in the inflow of said secondary heat exchange zone by restricting outflow from said zone and the flow to the primary heat exchange zone is controlled by being responsive to pressure conditions within the primary fractionator. Yet another aspect of this invention relates to the control of overhead from a tractionator as above wherein at least part of the split overhead can be passed through the primary heat exchange zone and at least part bypasses said zone and passes directly to said accumulator due to means responsive to the pressure in said accumulator, passing a separate portion of said split overhead through said secondary heat exchange and controlling the flow therethrough by a flow controller, and splitting the outflow of said second heat exchange zone so that it passes either in whole or in part through a first line connecting the first heat exchange zone or in whole or in part a second line directly connecting the accumulator, said second line containing flow controlling means which are responsive to temperature variation in the accumulator. In another aspect, this invention relates to thermal conservation and control by utilizing two heat exchange zones, a first zone associated with a primary fractionator and a second zone associated with a secondary fractionator, thorugh which part or all of the overhead of the primary fractionator may pass, said zones each being associated with an accumulator, the accumulator associated with the outflow of the second heat exchange zone controlling the amount of flow of overhead to the accumulator associated with the inflow of the first heat exchange zone by means of level controllers in the second heat exchange zone accumulator and fiow controllers responsive to the temperature in the first heat exchange zone accumulator. Yet another aspect of this invention relates to the control of reflux created from the overhead of a fractionator by splitting the overhead thereof to pass through two separate heat exchange zones, the first of which is directly connected to an accumulator, the second of which is connected directly to the first heat exchanger and directly to the accumulator so that the outflow of the second heat exchange zone may, due to flow control means associated with the inflow and outflow of said second heat exchanger, pass all of the outflow of said second heat exchange zone directly to the first heat exchange zone or pass all of said "ice outflow through accumulator temperature sensing and control means directly to the accumulator or pass a part of said outflow directly to the first heat exchange zone and part directly to the accumulator. Yet another aspect of this invention relates to the control of flow of material through a heat exchanger by means of either an accumulator with level control means therein and associated with the outflow of said heat exchanger or an accumulator with level control means therein which level control means are associated with a flow control means adjusted to vary the inflow to said heat exchanger in response to variations of level which are sensed by the level control means and passed on to the flow control means. In another aspect of this invention, the rate of flow of condensate from a heat exchanger which receives at least a part of the overhead of a fractionator is controlled by means of splitting this condensate by a flow control means responsive to the inflow of the heat exchanger that creates the condensate so that all or part of the condensate may pass directly to another heat exchanger and then to an accumulator or all or part of the condensate may pass directly to an accumulator.

In petroleum refining operations, very large capacities are utilized in order to achieve a large output for the sake of overall efiiciency and economy. In operations of this type, a tremendous amount of thermal energy is necessary not only to merely heat a large bulk of material that is constantly flowing through the apparatus but also to provide the energy required to separate the hydrocarbon feed into the separate fractions desired. Since the apparatus is very large and the amount of material treated is equally as ponderous and since such operations customarily function 24 hours a day, 7 days a week, the fuel requirements to supply the thermal energy necessary is of an exceedingly large proportion. Thus, it is highly desirable to eflect even the slightest amount of thermal conservation because this slight amount will be multiplied many times in the course of this day and night operation. For these reasons, a constant and never-ending struggle is waged against the inefiicient or wasteful use of fuel and the heat generated therefrom. It can be seen, then, that any increase in the efliciency of such operation is, due to magnitude of the operation, a significant contribution to the industry and mankind, not only from a technological point of view, but also from physical considerations.

The present invention provides a system which is applicable to any fractionation or distillation operation wherein a feed material is separated into its various components and is especially amenable to petroleum refining operations such as that discussed hereinabove. Although it is known in the art that passing overhead from a fractionator through a heat exchanger before passing said overhead to an accumulator or, alternatively, responsive to temperature control means in the accumulator, passing the overhead directly to said accumulator, this invention provides a system whereby optimum overall operating conditions are maintained, and even improved, due to a very significant conservation and transfer of thermal energy within the system, thus effecting not only improved flow control from the fractionator overhead, but also improved overall operating efficiency, with a consequent cost savings.

Accordingly, it is an object of this invention to provide improved method and apparatus for fractionation. Another object is to provide improved thermal conversion and thermal control in fractionation. Another object of this invention is to provide a more efiicient and economical temperature control system in a fractionation complex.

Other aspects, objects and the several advantages are apparent from a study of this disclosure, the drawings and the appended claims.

In one of its inventive concepts, this invention provides method and apparatus whereby a fractionator overhead is 3 split responsive to conditions in the fractionation zone, a first portion passing directly to a heat exchange zone which is, in turn, connected to ,a collecting zone for said fractionation zone, a second portion passing in heat exchange relationship with a separate fractionation zone which condenses the second portion transferring the heat thereby evolved to the second fractionation zone. The condensate of the secon-d portion is then, itself, split into at least two portions responsive to at least part of the inflow of the second heat exchange zone. All or part of the stream condensate from the second heat exchange zone may pass directly to the first heat exchange zone, thus eooling the material being treated by said heat exchange zone, or all or part of said condensate may pass directly to the collecting zone, thereby bypassing the first heat exchange zone. Whether or not the condensate passes directly to the collecting zone, it can be suitably controlled, .being responsive to temperature changes in the collecting zone itself. Thus, it can be seen that a part of the overhead from the fractionation zone is used not only to heat a separate zone or apparatus, but also to control thetemperature of itself, so to speak, before entering a collecting or accumulating zone from which is drawn 4 prior to introduction into accumulator 16. Valve 30' is controlled by any suitable flow control means 27 which, in turn, is responsive to the flow of material through line 2 at section 32. Valve 29. is controlled by temperature responsive means 17 which may be connected either to line 31 or directly into accumulator 16. Line 7 contains bypass line 13 in which a flow is controlled by means 14 which is responsive to the pressure in accumulator 16.; Accumulator 16 has an association with level controller '19 which, due to line 20, operates to control the flow of heat exchanger 21. The bottom flow from accumulator 16 passes via line 24 and pump 25 either as productthrough line 26 or as reflux through line 11, or both. The amount of flow of product through line 26 is controlled by flow responsive means 27 and the amount of reflux in line 11 is controlled by flow control means 12. Fractionator 57 has associated therewith external heating means 36 connected to heat exchanger 38. The flow of heating material through line 36 is controlled by valve 37 which is responsive via line 39 at temperature controller 40 to the temperature in fractionator 57. Fractionator 57 also has associated therewith feed means 41 and bottom flow means 59. Bottom flow means 59 is controlled in accordreflux for the fractionation zone from whence the overhead originally came. The control of outflow from the heat exchange zone associated with the separate fractionation zone or other heat accepting zones by response to the inflow to said heat exchange zone may be utilized under most all operating conditions. However, this arrangement is preferably utilized when the rate of flow of overhead vapors to said heat exchange zone is limited to some degree.

In another inventive concept of this invention, a flow control method and apparatus is provided which, under certain circumstances, may be substituted for the abovedjsclosed inflow responsive control valve. According to this concept, the outflow from the fractionation zone as-' sociated heat exchange zone is provided with a collection or accumulation zone which, in turn, is provided with a level control which controls the outflow of the collection or. accumulation zone. Thus, when an unlimited supply of vapors is passed to said heat exchange zone, flow control is perfectly achieved by use of the above-mentioned accumulation zone in lieu of or in conjunction with said inflow responsive flow, control. Referring now to the drawing .forifurther detail and disclosure: FIGURE 1 discloses diagrammatically a preferred form 9f this invention, including a fractionator whose overhead is split and passed to dual heat exchangers, one of which is associated with a separate fractionator, both of which combine to introduce to an accumulator an overhead material which will maintain the accumulator at a constant. temperature. I

FIGURE 2 discloses an accumulator used in conjunction with a .fractionator associated heat exchanger for purposes of flow control. v More, specifically, FIGURE 1 discloses a fractionator 1 to which is introduced feed 3 and heat through heat exchanger21. The bottom flow from fractionator 1 is passed through line 4 and is controlled by means of level control 22 and line 23. The overhead from fractionator 1 can be split into two portions, a first portion passing through lines 5 and 7 to heat exchanger 15 and being controlled by valve 6 which is responsive to the pressure in fractionator-l by means of elements 8, 9 and 10. The second portion travels through line 2 to tfractionator 57 which contains heat exchanger 58-. The overhead portion from line 2 passes through heat exchanger 58, thus condensing said overhead portion and transferring heat to fractionator 57. The condensate from heat exchanger 58 passes through line 28 and valve 29 to line 31 and, therefore, directly into accumulator 16. Also, either part or all of the condensate from heat exchanger 58 may pass through valve 30 and line 33 to line 7 totherein mix with the first portion "or 'said overhead and pass through heat exchanger ance with the level of liquid in the bottom of fractionator 57 by means of level controller and line 34. The overhead from fractionator -57 passes via line 42, valve 44 and line 45 to heat exchanger 47. Flow of overhead in lines 42 and 45 is controlled by pressure controller 43 in response to the pressure in fractionator 57. The outflow from heat exchanger 46 passes to accumulator 47 and from there via line 49, pump 50 and line 51 to either line 54 or line 53, or both. The amount of flow of product in line 54 is regulated by valve 56 which is responsive via line 55 to level controller 48 associated with accomulator 47. The flow of reflux in line 53 is controlled by flow con troller 52.. From the foregoing, it can be seen that the over head from cfractionator 1 is split into two fractions, one

fraction of which goes to the accumulator for rfraction'ator 1, the second fraction of which goes to a heat exchanger to aid in heating fractionator 57. The outflow from the heat exchanger 58 and fractionator 57 is then either passed in toto to heat exchanger 15 or all or part is passed, depending upon the amount of flow in line 2, into accumula tor 16 without further heat exchange treatment. The am amount of flow condensate directly to accumulator 16 is controlled by means which is responsive to the temperature in accumulator 16, Therefore, it can be seen that, depending upon the temperature in accumulator 16, more or less condensate may be passed directly from heat exchanger 58 to accumulator 16 thereby maintaining accumulator 16 at a constant temperature. For purposes of illustration, if the condensate from heat exchanger 58 is at a temperature higher than the condensate flowing [from heat exchanger 15 through line 31 to accumulator 16, then, if the temperature in accumulator 16 is at the desired level or high er, the condensate from heat exchanger 58 will be passed, due to the closing of valve 29 through line 33 into line 7 so that it will be cooled in heat exchanger 15. If, on the other hand, the temperature in accumulator 16 is below the desired level, valve 29 will be opened and some of the higher temperature condensate from heat exchanger 58 will pass via line 28 directly to line 31 and, therefore, directly to accumulator 16 to thus increase the temperature therein.

Itis, of course, obvious and within the scope of this invention for the reverse procedure to also be used, i.e., the temperature of the condensate from heat exchanger 58 being at a lower temperature than the temeprature of the condensate from heat exchanger 15, thus necessitating the use of line 33 when it is desired to raise the temperature in accumulator 16 or the use of line 28 when it is desired to lower the temperature in accumulator r16.

' FIGURE 2 discloses the use of an accumulator 60 in lieu of the flow controller 27 of FIGURE 1. The portion of the overhead from fractionator 1 which passes into line 2 also passes through heat exchanger 58 to fractionator 57 in order to also contribute heat to the operation in fractionator 57. The outflow from heat exchanger 58 passes via line 28 into accumulator 60 and from accumulator 60 through line *63 and valve 62 into line 28. The flow of condensate from accumulator 60 is controlled by valve 62 which, in tum, is responsive by means of level control- 'ler 61 to the level of liquid in accumulator 60.

It should be noted that, in the operation of this invention, the rate of flow of overhead vapors through, for example, line 2 of FIGURE 1, will generally be maintained so that there will usually be some vapors flowing through the heat exchanger connected to that line.

It will be understood that the flow diagram presented and described as a part of the disclosure is schematic only and that many additional conventional pieces of equipment, such as valves, pumps, heat exchangers and the like, will be necessary for any :particular installation, and can be supplied to meet the requirements of the particular case by anyone skilled in the art.

In order to more fully describe this invention, reference will be made to specific operating conditions for both that apparatus depicted in FIGURE 1 and the apparatus of FIGURE 1 when modified in accordance with FIGURE 2.

The rates and conditions of operation of apparatus similar to that shown in FIGURE 1 is as follows:

EXAMPLE I No. 57 column RATES Volumes Stream G.p.d.

Feed (iso-butane, n-butane and about 3% by weight propane) Overhead fraction (iso-butane, propane and small amount of n-butane) 160, 000 3,80 Bottom traction (n-butane and small amount of propane and iso-butane) 340, 000 8,200 Reflux of No. 57 column overhead--- 1 850 000 44, 000

Steam to heat exchanger (38) No. 1 column overhead to reboiler (58) 1 Pounds per hour.

CONDITIONS Points in apparatus Pressure Tempera- (P.s.i.g.) ture F.)

Column kettle 145 183 Column top 135 153 Accumulator (47) 110 110 No. 1 column overhead to reholler (58)-.- 38 263 Vapor Condensate irom reboller (58) .1 35 258 Rates and c0nditionsNo. 1 column RATES Volumes Streams G.p.d. B.p.d

Feed (Predominantly iso-heptaue and n-heptane). 175,000 4, 150 Overhead fraction (iso-heptane) 45,000 1,070 Bottom traction (n-l'leptane) 130,000 3, 080 Reflux of No. 1 column overhead 670,000 15, 900 Steam to heat exchanger (21) 1 38, 000 No. 1 column overhead to reboiler (58) 650, 000 15, 500

1 Pounds per hour.

boiler (58) can be limited in two ways.

(1) If the rate to the reboiler is set greater than the total overhead vapor flow [from No. 1 column, the pressure on No. 1 column will drop. A light and horn signal can be provided to warn the operator before this occurs and any time the alarm system actuates, the operator can reduce the flow rate to the reboiler until the column pressure motor valve returns to a control range.

(2) If the rate of flow to the reboiler is increased beyond the capacity of the reboiler bundle, the recorded flow rate (27) will become erratic as a result of uncondensed vapor entering the liquid line and motor valve on the reboiler outlet. This can be correlated with the outlet liquid temperature which can be indicated on a potentiometer console. This can occur when the outlet temperature from the reboiler reaches approximately 260 F. To correct this situation, the rate of flow to the reboiler can be reduced slightly until the outlet temperature reaches approximately 258 F. or until the recorded flow rate becomes smooth.

It can be seen from the above that not only is the steam consumption of the overall system reduced, but also there will be a noticeable reduction of cooling load on heat exchanger 15. It will also be noted from the above that, since the condensate from reboiler 58 is at a temperature of 258 F it is at a higher temperature than the overhead from fractionator 1 that has passed through heat exchanger 15 which is at a temperature of F. Thus, referring to FIGURE 1, in this particular example, it will be seen that, in order to raise the temperature in accumulator 16, the outflow from reboiler 58 will 'be passed through line 28 to line 31 and, if the temperature in accumnlator 16 is desired to -be lowered, the outflow from reboiler 58 will be passed through line 33 to line 7 for treatment by heat exchanger 15.

The following will specifically describe rates and conditions and apparatus such as that shown in FIGURE 1 as modified in the manner shown in FIGURE 2.

EXAMPLE II No. 57 column The normal operating conditions and rates were kept the same except that the steam rate was reduced by using vapors from No. 1 column overhead stream. The feed rate was 300,000 gallons per day (g.p.d.) or 7,150 barrels per day (b.p.d.).

1 Pounds per hour.

CONDITIONS Points in Apparatus Pressure Tempera- (p.s.i.g.) ture.( P.)

Column kettle 72 205 Column top 65 177 Accumulator (47) 45 138 No. 1 column overhead to rehoiler (58) 23 258 Vapor condensate from reboiler (58) 20 250 Rates and conditions-N 0. 1 column RATES Volumes Streams G.p.d. Bpd.

Feed (n-hexane, n-heptane and iso-heptane) 350,000 8, 350 Overhead fraction (n-hexane) 128,000 3, 050 Bottom fractions (n-heptane and iso-heptane) 222, 000 5, 300 Reflux of No. 1 column overhead 440, 000 10, 500 Steam to heat exchanger (21) l 28, 000 No. 1 column overhead to reboiler (58) 370, 000 8, 800

1 Pounds per hour.

CONDITIONS Points in Apparatus Pressure Tempera- (p.s.i.g.) ture F.)

Column kettle 28 300 Column top 25 258 Overhead to reboiler (58) 23 258 Condensate from reboiler (58). 20 20 Overhead to heat exchanger (l5) 13 2:15 Overhead from heat exchanger (l5) 8 120 Accumulator (16) 6 13d Accumulator (60) RATES Stream-Overhead condensate from accumulator; volume-250 gal. per minute.

CONDITIONS Points in A paratus Pressure Temperap (p.s.i.g.) ture F.)

Interior of accumulator "l 20 250 The maximum flow rate to No. 57 column vapor reboiler (58) can be limited in two ways.

(1) If the rate to the reboiler is set greater than the total overhead vapor flow from No. 1 column, the pressure on No. 1 column will drop. A light and horn signal can be provided to warn the operator before this occurs, and any time the alarm system actuates, the operator can reduce the flow rate to the reboiler until the column pressure motor valve returns to a control range. (This should occur only when No. 1 column feed and reflux rates are lower than normal.)

(2) If the rate of flow to the reboiler is increased beyond the capacity of .the reboiler bundle to condense the vapor, the recorded flow rate will become erratic as a result of uncondensed vapor entering the liquid line and motor valve on the reboiler outlet. This can be correlated with the outlet liquid temperature which can be indicated on a potentiometer console. This will occur when the outlet temperature from the reboiler reaches approximately 255 F. To correct this situation, the rate of flow to the reboiler can be reduced slightly until the outlet temperature reaches approximately 250 F. or until the recorded flow rate becomes smooth. (This should occur only when the condensate level control is out of service or is not on control.)

' From the foregoing, it can be seen that the outflow from accumulator 60 is at a temperature, lower, 255 F., than the overhead product from fractionator 1 entering heat exchanger 15 and higher, 120 F., than the overhead prod- .8. not leaving heat exchanger 15. Thus, it is again clear that,

' in order to increase the temperature in accumulator 16,

the flow from accumulator 60 will be directly introduced into accumulator 16 whereas, in order to lower the temperature in accumulator 16, the outflow from accumulator 60 will be first passed through heat exchanger 15.

, As the level in accumulator 16 recedes, level controller 19 will allow, by means of line 20 and valve 20, an increased flow of heat by means of line 21 to fractionator 1.

This increased flow of heat to fractionator 1 will increase the flow of material to accumulator 16 through lines 5 and 7 and possibly 13 due to increased pressure in fractionator 1 as sensed by pressure response control 9, which, in turn, opens valve 6.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, the drawings, and the appended claims by one skilled in the art in possession of this disclosure of the foregoing invention.

I claim:

1. A method of fractionation of hydrocarbons comprising fractionating in a first fractionation zone a feed hydrocarbon into an overhead fraction and a bottom fraction, splitting said overhead fraction into two streams, passing a first stream to a first heat exchange zone, controllingthe amount of flow of said first stream to said first heat' exchange zone by a means responsive to pressure variations within the first fractionation zone, passing a second stream to a reboiling zone associated with a second fractionation zone in such a manner that heat from said reboiling zone is passed directly to said second fractionation zone, withdrawing said second stream from said reboiling zone, splitting said withdrawn second stream into two portions by means responsive to the amount of flow of said second stream prior to entry into said reboiling zone,

adding a first portion of said two portions to said first stream when said first stream leaves said first heat exchange zone, varying the amount of said first portion that is added to said first stream by means responsive to the temperature of the composite of said first stream and any of said first and second portions added to said first stream upstream or downstream of said first heat exchange zone,

said temperature being measured downstream from said first heat exchange zone, passing a second of said two portions to said first stream prior to the entry of said first stream into said first heat exchange zone and passing the outflow from said first heat exchange zone and any added first portion to a collecting zone.

2. -A method according to claim 1 wherein operating 7 1 heat supplied to said first fractionation zone is varied in response to level variations in said collecting zone, wherein at least part of said first stream bypasses said heat exchange zone to thereby pass directly into said collecting zone in response to pressure variations in said collecting 1 zone.

prising first fractionation means for separating a feed into a first and a second fraction, means for dividing at least one of said fractions into a first and a second stream, first cooling means for cooling said first stream, means for controlling the flow of said first stream which is responsive to the pressure in said first fractionation means, second cooling means for cooling said second stream and for transferring the heat evolved therefrom to a second fractionation means, means for controlling the outflow from said second cooling means which is responsive to the inflow to said second cooling means, means for splitting the outflow from said second cooling means into two portions, means for passing a first portion of said two portions to said first stream prior to entry of said first stream into said first cooling means, means for passing a second portion of said two portions into said first stream after said first stream and any added first portion has passed through said first cooling means, means for controlling the amount of said second portion passing into said first stream and any added first portion after said first stream and any added first portion has passed through said first cooling means which is responsive to the temperature of the mixture of said first stream and any portions of said second stream added thereto, a receiving means to receive a mixture of said first stream and any portions of said second stream added thereto, level control means on said receiving means for varying the amount of operating heat supplied to said first fractionation means in response to level variations in said receiving means, and means for bypassing said first cooling means with said first stream which is responsive to pressure conditions in said receiving means.

4. Apparatus according to claim 3 wherein means is provided for passing at least part of the overhead fraction from said second fractionator and at least one intermediate fraction from said second fractionator to said first fractionation means and means is provided in and with said first fractionation means to utilize said second fractionator overhead and intermediate fractions as at least one of reflux, additional feed and feed diluent in said first fractionation means.

5. A fractionation method comprising fractionating in a first fractionation zone a feed material to produce at least an overhead fraction, splitting said overhead fraction into at least two streams, passing one of said at least two streams to a first heat exchange zone, controlling the flow of said first stream to said first heat exchange zone by means responsive to pressure variations within said first fractionation zone, passing a second stream of said at lea-st two streams to a reboiling zone in a second fractionation zone, withdrawing said second stream from said reboiling zone, splitting said withdrawn second stream into at least two portions by means responsive to the rate of flow of said second stream into said reboiling zone, adding a first portion of said at least two portions to said first stream after said first stream leaves said first heat exchange zone, varying the amount of said first portion that is added to said first stream by means responsive to the temperature of the composite of said first stream and any of said first and second portions added to said first stream either upstream or downstream of said first heat exchange zone, and passing a second of said at least two portions to said first stream upstream of said first heat exchange zone.

6. Fractionation apparatus comprising a first fractionation means for separating a feed into at least a first and a second fraction, means for dividing at least one of said fractions into a first and a second stream, first cooling means for cooling said first stream, means for controlling the flow of said first stream which is responsive to the pressure in said first fractionation means, second cooling means for cooling said second stream, means for controlling the outflow from said second cooling means which is responsive to the inflow to said second cooling means, means for splitting the outflow from said second cooling means into at least two portions, means for passing a first portion of said at least two portions to said first stream prior to entry of said first stream into said first cooling means, means for passing a second portion of said at least two portions into said first stream after said first stream and any added first portion has passed through said first cooling mean-s, means for controlling the amount of said second portion passing into said first stream and any added first portion after said first stream and any added first portion has passed through said first cooling means which is responsive to the temperature of the mixture of said first stream and any portions of said second stream added thereto.

7. Apparatus comprising a fractionation means, a first heat exchange means, a second heat exchange means con nected with the interior of said fractionation means and having an outlet means, accumulator means operatively connected to the outlet means of said second heat exchange means, said accumulator means having a liquid level control means connected thereto and to the outlet end of said accumulator means, conduit means connecting the outlet end of said accumulator means to the downstream end of said first heat exchange means, and temperature responsive means connected between the downstream end of said first heat exchange means and said conduit means so that the flow rate of fluids through said conduit means is controlled by the temperature at the downstream end of said first heat exchange means.

References Cited UNITED STATES PATENTS 2,781,293 2/1957 Ragatz 196132 X 3,215,744 1l/1965 Frank 203- X 3,228,860 1/1965 Larson 62-2l X 3,260,057 7/1966 Becker 20398 X 3,281,337 10/1966 Zahnstecker et al. 202- X FOREIGN PATENTS 1,305,938 11/1961 France.

NORMAN YUDKOFF, Primary Examiner. F. E. DRUMMOND, Assistant Examiner, 

1. A METHOD OF FRACTIONATION OF HYDROCARBONS COMPRISING FRACTIONATING IN A FIRST FRACTIONATION ZONE A FEED HYDROCARBON INTO AN OVERHEAD FRACTION AND A BOTTOM FRACTION, SPLITTING SAID OVERHEAD FRACTION INTO TWO STREAMS, PASSING A FIRST STREAM TO A FIRST HEAT EXCHANGE ZONE, CONTROLLING THE AMOUNT OF FLOW OF SAID FIRST STREAM TO SAID FIRST HEAT EXCHANGE ZONE BY A MEANS RESPONSIVE TO PRESSURE VARIATIONS WITHIN THE FIRST FRACTIONATION ZONE, PASSING A SECOND STREAM TO A REBOILING ZONE ASSOCIATED WITH A SECOND FRACTIONATION ZONE IN SUCH A MANNER THAT HEAT FROM SAID REBOILING ZONE IS PASSED DIRECTLY TO SAID SECOND FRACTIONATION ZONE, WITHDRAWING SAID SECOND STREAM FROM SAID REBOILING ZONE, SPLITTING SAID WITHDRAWN SECOND STREAM INTO TWO PORTIONS BY MEANS RESPONSIVE TO THE AMOUNT OF FLOW OF SAID SECOND STREAM PRIOR TO ENTRY INTO SAID REBOILING ZONE, ADDDING A FIRST PORTION OF SAID TWO PORTIONS TO SAID FIRST STREAM WHEN SAID FIRST STREAM LEAVES SAID FIRST HEAT EXCHANGE ZONE, VARYING THE AMOUNT OF SAID FIRST PORTION THAT IS ADDED TO SAID FIRST STREAM BY MEANS RESPONSIVE TO THE TEMPERATURE TO THE COMPOSITE OF SAID FIRST STREAM AND ANY OF SAID FIRST AND SECOND PORTIONS ADDED TO SAID FIRST STREAM UPSTREAM OR DOWNSTREAM OF SAID FIRST HEAT EXCHANGER ZONE, SAID TEMPERATURE BEING MEASURED DOWNSTREAM FROM SAID FIRST HEAT EXCHANGE ZONE, PASSING A SECOND OF SAID TWO PORTIONS TO SAID FIRST STREAM PRIOR TO THE ENTRY OF SAID FIRST STREAM INTO SAID FIRST HEAT EXCHANGE ZONE AND PASSING THE OUTFLOW FROM SAID FIRST HEAT EXCHANGE ZONE AND ANY ADDED FIRST PORTION TO A COLLECTING ZONE. 